Statistical properties of the nebular spectra of 103 stripped envelope core collapse supernovae

TL;DR

This study analyzes the nebular spectra of 103 stripped envelope supernovae to understand their ejecta geometry, expansion velocities, and progenitor core masses, revealing common asymmetries and correlations with progenitor properties.

Contribution

It provides a comprehensive analysis of nebular spectra for a large supernova sample, linking spectral features to progenitor mass and explosion dynamics, and classifies ejecta geometries.

Findings

Deviation from spherical symmetry is common in all supernova types.

A correlation exists between [O I] width and [O I]/[Ca II] ratio, indicating more massive cores expand faster.

The [O I]/[Ca II] ratio influences ejecta geometry, with higher ratios favoring Gaussian profiles.

Abstract

We present an analysis of the nebular spectra of 103 stripped envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O I] 6300, 6363. The line profile and width of [O I] are employed to infer the ejecta geometry and the expansion velocity of the inner core. These two measurements are then compared with the SN sub types, and further with the [O I]/[Ca II] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best fit results of the [O I] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at about 1 sigma level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O I] width and [O I]/[Ca II] ratio is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O I]/[Ca II] ratio increases, the fraction of objects with Gaussian [O I] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass.